Thin film wound dressings are widely used in the care of wounds. As disclosed in U.S. Pat. No. 3,645,835, such a dressing consists essentially of a thin film of polyurethane or other suitable elastomer that is capable of transmitting moisture vapor at rates approximating or exceeding those of skin. Such a film is coated along its underside with a pressure-sensitive adhesive that, because of its composition or discontinuity, or both, is also vapor permeable. The result is a dressing that is often referred to as being "breathable," is capable of flexing and stretching and of maintaining a moist environment for a healing wound, and provides a protective bacterial barrier for such a wound.
Because of their flexibility and stretchability, thin film dressings are also useful for other purposes, such as providing protective covers over injection and catherization sites. Such a cover or dressing may readily conform to the contours of a catheter and those of the skin surfaces at an application site, while allowing visual inspection of the site and protecting it against contamination.
Offsetting those advantages is the disadvantage that thin film wound dressings may be difficult to apply, especially for one person. Since such a film is not self-supporting, some means must be provided to prevent it from becoming folded and wrinkled, and adhering to itself, during application. In general, two types of removable "delivery systems" have been developed to support such a dressing as it is delivered from the package to the site of application.
One such support system may be referred to as a removable frame system, and the other as a removable film system. In a removable frame system, a thin film wound dressing is supported by a removable peripheral frame as disclosed, for example, in U.S. Pat. No. 4,372,303 and EP 0 051 935. The frame functions as a device to hold the dressing in generally planar condition until it has made adhesive contact with the attachment site, at which time the frame is ordinarily removed. Such a frame system has the advantage of allowing the transparent film to flex and stretch within the opening of the frame, thus allowing the dressing to conform to the contours of body surfaces, catheters, and the like.
One disadvantage of the frame system is that it is often difficult and time-consuming to remove the frame after the dressing has been applied. Quite commonly such a frame does not peel easily from the film in a single motion but instead must be carefully "teased" away from the edges of the dressing. Another disadvantage of frame systems is that they do not work well should the user wish to cut the dressing to smaller size, since the frame must remain intact for ease of application.
In a film system, the entire upper surface of the dressing has a reinforcing cover that may be peeled away after the dressing is applied. To facilitate application of the dressing, the cover is usually a transparent film, but one that does not have the extensibility and low tensile modulus of the dressing itself. While such a delivery system has the advantage (over a frame system) that the supporting cover may be peeled away easily in one step, it has the disadvantage that the central portion of the dressing is held in relatively stiff condition and cannot readily conform to the irregular or uneven surfaces to which it must be applied. Also, such a support system does not work well if the dressing is to be cut to a smaller size because it may be difficult, sometimes impossible, to start the peel of the cover away from the dressing if the removal tab of the cover is not part of the cut piece.
Accordingly, a main aspect of this invention lies in providing a thin film wound dressing with a flexible support backing that may be easily removed in one peeling motion whether the dressing is to be applied in its original size (as supplied) or as a smaller cut section or piece of the original dressing. The backing effectively supports the wound dressing during application, and, after the dressing has been applied, the backing may be easily gripped and peeled away without at the same time causing the dressing itself to become detached from the skin surfaces to which it has been adhered.
Like prior thin film wound dressings, the dressing of this invention comprises a thin breathable elastomeric film of polyurethane or some other material having similar properties. The underside of the film is coated with a gas-permeable adhesive layer which in turn is covered by a removable release liner of siliconized paper or similar material. The opposite surface of the elastomeric film has a foraminous backing layer of flexible and preferably stretchable material. specifically, the backing layer has a multiplicity of wide openings separated from each other by narrow strip portions of the backing layer. Ideally, at least some of the strip portions terminate in free ends located along a peripheral edge of the elastomeric film.
The flexible backing layer is removably attached to the upper surface of the elastomeric film. A releasable attachment may take the form of a pressure-sensitive adhesive or a thermal bond. In either case, the strength of the bond between the flexible backing and the film should be greater than the strength of an equal area of the adhesive bond between the film and the removable release sheet or liner. Most advantageously, the liner protrudes beyond an edge of the film and an imperforate portion of the backing directly thereabove, with the result that the release liner may be easily peeled away from-the film without disrupting the bond between the film and its flexible backing. However, once the dressing is in place, the flexible backing may itself be peeled away from the film, without disrupting the adhesive attachment between the film and the patient's skin, because most of the backing is secured to the film only along the narrow strip portions of the backing. If at least some of the strip portions have free ends terminating along the edge of the film, a user may simply grip one of those free ends to initiate the peeling action for removing the backing from the applied thin film dressing. Alternatively, a user may grip one of the strip portions between the multiplicity of window openings in the foraminous backing and pull the strip portion upwardly to commence peeling of the backing from the applied thin film dressing.
In a preferred embodiment, the flexible foraminous support backing has a generally imperforate first tab portion that extends beyond the film along at least a portion of its periphery, and the release liner projects outwardly beyond that tab portion and well beyond the peripheral edge of the film. The backing layer may include a generally imperforate second tab portion that is connected to a plurality of the strip portions and is located outwardly beyond an edge of the film opposite from the first tab portion. The release liner may be easily peeled away from the rest of the dressing by commencing the peeling action in the area of the first tab portion and then, after the dressing has been applied, the removable backing layer may be peeled away from the applied film by drawing back on the second tab portion.
To assist a user in ascertaining the tab portions for the proper sequence of the first and second peeling steps, such tab portions are preferably provided with suitable alphanumeric indicia. A particularly effective way of doing so takes the form of providing the respective tab portions of the removable support backing with distinctive alphanumeric cutouts indicating the proper sequence for the successive peeling steps.
The openings in the backing layer may be regular or irregular in shape and should be of an average size within the range of about 0.5 cm.sup.2 to about 9 cm.sup.2, with a preferred area averaging about 1 cm.sup.2 to about 4 cm.sup.2. In one embodiment, such openings have the shape of an equilateral rectangle (i.e., are generally square) but in other embodiments such openings may be of the shape of other substantially regular polygons (i.e., hexagon, octagon, etc.) or may be rounded (e.g., oval or circular) or a combination of rounded and non-rounded. It is important that such openings, or at least a large proportion of them, be wide in contrast to elongate; that is, two cross dimensions of such an opening measured at right angles should be approximately the same so that the strip portions between those openings will provide adequate support for the thin film of the dressing and still define openings large enough, and regular enough, that a user may insert his/her fingers into the openings to grasp a strip portion of the backing in order to peel that backing away from the film.
The removable and formaminous support backing must be flexible and, in a preferred embodiment, takes the form of a soft, flexible polymeric foam. While the backing layer may or may not be stretchable, stretchability is considered highly desirable. Where a stretchable backing layer is used, the extensibility of the backing layer without breaking should be to at least 120% of its original length, preferably to at least 150% of its original length. Also, its modulus should be low enough so that the support backing does not objectionably reduce the stretchability and conformability of the film when the dressing is being applied. To that end, the material of the support backing should be capable of extending to 110% of its original length with a force of less than about 1000 pounds per square inch, preferably less than about 500 pounds per square inch, when tested at an extension rate of 10 times the sample length per minute.
The strip portions between the openings of the support backing should have a width generally falling within the range of about 1 mm to about 4 mm, and the thickness of the backing layer should be in the range of about 0.2 mm to about 2.0 mm (preferably 0.5 mm to 1.0 mm). By virtue of its thickness, the support backing greatly increases the bending modulus of the dressing, thereby making it self-supporting.